FIG. 1 shows a prior art luminance/chrominance separating apparatus (hereinafter referred to as "Y/C" separator) which is conventionally used in a video signal processing circuit of such television receivers. The Y/C separator is implemented by a well-known three-dimensional Y/C separation technique using components of the video signal in the horizontal axis, the vertical axis and the time axis.
In FIG. 1, a composite video signal is input to an input terminal 800 and then supplied to a luminance component separator (hereinafter referred to as Y processing unit) 801 and a chrominance component separator (hereinafter referred to as C processing unit) 802.
The Y processing unit 801 includes a stationary Y processor 811 and a moving Y processor 812, which are disclosed in the "ITEJ Technical Report", Vol. 12, No. 51, pp. 106 (Nov., 1988). These processors 811 and 812 are suited for separating the Y component in stationary pictures and moving pictures, respectively. The stationary and moving Y components are selectively applied to a subtractor 814 through a switching unit 813.
The moving Y processor 812 comprises a line memory 821, a line memory 822, a correlation checking unit 823 and a band pass filter (band pass filter is hereinafter referred to as BPF) 824. The composite video signal on the input terminal 800 is applied to the line memory 821 wherein the composite video signal is delayed by one horizontal scanning period (hereinafter referred to as "1H" period). An output from the line memory 821 is supplied to the line memory 822 wherein the composite video signal is further delayed by the 1H period. The composite signals from the input terminal 800, the line memory 821 and the line memory 822 are applied to the correlation checking unit 823. The correlation checking unit 823 checks correlations among the three composite video signals so that an output therefrom represents uncorrelated signal components among the three composite video signals.
The uncorrelated signal components are applied to the BPF 824. The BPF 824 has a characteristic for passing a color subcarrier signal. Thus the uncorrelated signal components output from the BPF 824 are mainly chrominance components (hereinafter referred to as C components). The C components are applied to the switching unit 813.
The stationary Y processor 811 comprises a frame memory 825, a subtractor 826 and a BPF 826. The composite video signal from the line memory 821 of the moving Y processor 812 is also applied to the frame memory 825 and the subtractor 826. In the frame memory 825, the composite video signal is delayed by one frame period. In the subtractor 826, the composite video signals from the line memory 821 and the frame memory 825 are subtracted from each other. Thus an output from the subtractor 826 also represents uncorrelated components between the two composite video signals.
The uncorrelated signal components from the subtractor 826 are applied to the BPF 827. The BPF 827 has also such a characteristic for passing a color subcarrier signal. The signal extracted by the BPF 827 is applied to the switching unit 813.
The switching unit 813 selectively outputs either the signal from the stationary Y processor 811 or the signal from the moving Y processor 812 under the control of a motion detector 805. The motion detector 805 outputs a signal representing a motion of a picture in the composite video signal, as disclosed in the U.S. Pat. No. 4,626,891. When there occurs a motion in the picture, a signal, e.g., a logic level of "1" representing the motion causes the switching unit 813 to output the signal from the stationary Y processor 811. When there occurs non-motion in the picture, another signal, e.g., a logic level of "0" representing the non-motion causes the switching unit 813 to output the signal from the moving Y processor 812.
The selected signal from the switching unit 813 is applied to the subtractor 814 wherein it is subtracted from the composite video signal from the line memory 821. The signal from the switching unit 813 represents the C component, as described above. Thus, a luminance component (hereinafter referred to as Y component) is obtained.
The C processor 802 includes a color demodulator 831, a time-division multiplexer 832, a stationery C processor 838, a moving C processor 833 and a switching unit 837, as also disclosed in the above-mentioned "ITEJ Technical Report". These processors 838 and 833 are suited for separating the C component in stationary pictures and moving pictures, respectively. The stationary and moving Y components are selectively output through the switching unit 837.
The composite video signal on the input terminal 800 is also applied to the color demodulator 831 which demodulates I and Q signals as baseband signals of the chrominance components from the composite video signal. However, the outputs of the color demodulator 831 contain high frequency components of the Y components. The I and Q signals are multiplexed in a time-sequential form by the time division multiplex circuit 832 and then applied to the moving C processor 833.
The moving C processor 833 comprises a line memory 834, a line memory 835 and a correlation checking unit 836. The multiplexed signal output from the time division multiplex circuit 832 is applied to the line memory 834 wherein the multiplexed signal is delayed by 1H period. An output from the line memory 834 is supplied to the line memory 835 wherein the multiplexed signal is further delayed by the 1H period. The multiplexed signals from the time division multiplex circuit 832, the line memory 834 and the line memory 835 are applied to the correlation checking unit 836.
The correlation checking unit 836 checks correlations among the three multiplexed signals so that an output therefrom represents uncorrelated signal components among the three multiplexed signals. The uncorrelated signal components include mainly the I and Q components. The I and Q components are applied to the switching unit 837.
The stationary C processor 838 comprises a frame memory 839 and an adder 840. The multiplexed signal from the line memory 834 of the moving C processor 833 is also applied to the frame memory 839 and the adder 840. In the frame memory 839, the multiplexed signal is delayed by one frame period. In the adder 840, the multiplexed signals from the line memory 834 and the frame memory 839 are subtracted from each other. Thus an output from the adder 840 also represents uncorrelated components between the two multiplexed signals. The uncorrelated signal components from the adder 840 are applied to the switching unit 837.
The switching unit 837 selectively outputs either the signal from the stationary C processor 838 or the signal from the moving C processor 833 under a control of the motion detector 805. When there occurs a motion in the picture, the signal representing the motion causes the switching unit 837 to output the signal from the stationary C processor 838. When there occurs no motion in the picture, the signal representing the no motion causes the switching unit 837 to output the signal from the moving C processor 833. The selected signal from the switching unit 813 represents the I and Q components, as described above.
In the prior art Y/C separator, the Y component and the C component are separated by both the Y processor 801 and the C processor 802. Each of the processors 811 and 812 uses a frame memory which needs a huge memory capacity and thus is very expensive. Furthermore, the I and Q components obtained by the prior art Y/C separator are not able to directly couple to home VTRs such as VHS type VTRs, 8-mm type VTRs, etc.